It is well known that isocyanates may be added to isocyanate-reactive systems such as alkyd resins or acrylic resins to improve both the curing behavior and the properties of the cured coating. The preparation and use of urethane oils of this type are extensively discussed at pages 468 to 477 of Polyurethanes: Chemistry and Technology, Volume II Technology, Saunders and Frisch, Interscience 1964. It is also known that coatings prepared from aliphatic isocyanates impart superior light stability (resistance to yellowing, particularly on exposure to sunlight) as compared to aromatic isocyanates. A class of isocyanates which has been found to be particularly favorable for coating applications are aliphatic or cycloaliphatic polyisocyanates, especially the tris (isocyanato alkane) biurets such as those disclosed in U.S. Pat. Nos. 3,124,605 and 3,201,372. It has been found desirable to add such isocyanates to alkyd resin systems containing aliphatic solvents such as those used in the auto refinishing industry. Unfortunately, while these biuret-containing polyisocyanates, including the popular tris (isocyanato alkane) biurets, exhibit some degree of compatibility with the alkyd resins themselves, they display a high degree of incompatibility with the apolar solvents normally used in such systems. Since these solvents are both effective and economical in such systems, it was felt that the compatibility of the aliphatic polyisocyanates would have to be improved if they were to find practical utility in these systems.
In order to improve the compatibility of aliphatic biuret isocyanates with apolar solvents, it was proposed in concurrently filed application U.S. Ser. No. 282,206 filed July 10, 1981, to react these isocyanates with aliphatic or cycloaliphatic monohydroxy alcohols containing at least 8 carbon atoms. While these modified isocyanates exhibited increased compatibility with apolar solvents, they no longer formed storage stable solutions in the polar solvents normally used to lower the viscosity of isocyanates, since the isocyanate solvents are more polar than the apolar solvents used with the isocyanate-reactive systems.
It is therefore an object of the present invention to form polyisocyanate adducts which are compatible with apolar solvents and still maintain good storage stability in solution.
It is a further object of the present invention to provide polyisocyanate adducts which overcome the prior art problems associated with the use of isocyanates in isocyanate-reactive systems, such as alkyd resins or acrylic resins.